Posted by
led4you on Tuesday, April 08, 2008 1:07:21 AM
An LED is a Light Emitting Diode, and is a
semi-conductor device which will glow if you pass a current through it. A
semi-conductor is a material which in it's natural state won't conduct
electricity well, but if you add tiny quantities of other materials LED will conduct quite well.
Normally each atom in the semi-conductor
has 4 electrons and there are none free, but if you add a few atoms with 5
electrons there are some extra electrons which can move easily and carry a
current (an N-type semi-conductor). Similarly if you add some atoms with only 3
electrons and then you get some gaps which other electrons can move into (a
P-type semi-conductor). The electrons can now move a bit like the tiles in a
sliding tile puzzle, but it is easier to think of a positively charged hole
moving through the semiconductor.
.A diode is made if you join a lump of
P-type semi-conductor to a lump of N-type. If you make the N-type region
negative and the P-type positive, electrons and holes will move towards the
junction and there are plenty of charge carriers there and a current can flow.
But if you make the N-type region positive
and the P-type negative then electrons and holes will be pulled away from the
junction leaving the junction with nothing to carry current, so it becomes
insulating and a no current can flow.
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